Voice mail systems (also termed voice messaging systems) attach to the telephone network, often via a PBX, and are used to receive incoming calls when the intended recipient or subscriber is absent or otherwise engaged. Typically a greeting is played to the caller, who is then asked to leave a message for storage in the voice mailbox of that subscriber. Most systems allow the greeting to be personalised for each subscriber, and may include the subscriber speaking their own name. The intended recipient of the call can then dial up the voice mail system to listen to the stored messages from their mailbox at some future time. Such voice mail systems also usually allow messages to be sent or forwarded from one subscriber of the voice mail system to another.
A voice mail system is generally implemented either on special purpose computer hardware, or else on a standard computer workstation equipped with a suitable telephony interface. Such voice mail systems are well-known; one example is the DirectTalkMail system, available from IBM Corporation, which operates in conjunction with the DirectTalk/6000 voice processing system (also available from IBM).
Also very well-known are computer-implemented electronic mail (e-mail) systems, such as Lotus Notes, available from Lotus Corporation, whereby computer files, primarily textual, may be sent from one computer user to another. The recent development of the Internet has led to a great expansion in the use of such electronic mail systems. Typically computer e-mail systems have been separate from voice mail systems, the former usually being accessed via a desktop computer, the latter via a telephone. but in recent years unified mail systems have been developed which can handle both textual and voice messages (such systems are sometimes referred to as multimedia systems). For example, Lotus Notes includes Phone Notes whereby voice information entered via a telephone may be captured into a Note. Essentially Phone Notes is a development environment; it does not provide a full-scale multi-user voice messaging system.
W087/07801 discloses an integrated system which combines a voice mail system and a computer e-mail system. In this integrated system, the user may designate one mail system (ie voice or computer) as the primary recipient for all messages, with notifications of both voice and e-mail messages being received at this system. This approach is developed in U.S. Pat. No. 5,333,266, which teaches an integrated messaging system based on multiple servers for different media types. Commercially available products which provide integrated or unified messaging include CallXpress3 DeskTop for Windows, available from Applied Voice Technology Incorporated, and VMX DeskTop for Windows, available from VMX Incorporated (now part of Octel Communications Corporation). Another multimedia messaging system is Intuity from AT&T (see Computer Reseller News, Nov. 28, 1994, p12).
The recent development of the Internet has also led to its use for telephony, as described for example in "Dial 1-800-Internet" in Byte Magazine, February 1996, p83-86, and in "Nattering On", in New Scientist, Mar. 2, 1996, p38-40. Such Internet telephones sometimes provide a voice mail or answerphone type function. Patent application GB 9604667.7 (UK9-96-015), by IBM Corporation, describes the provision of a full voice mail service for such Internet telephones.
It is known to have multiple voice mail systems connected together. One reason for doing this is to provide extra capacity, as well as a redundancy capability, to provide back-up should one of the voice mail systems be unavailable. For example, U.S. Pat. No. 5,029,199 discloses an architecture with multiple voice mail units, connected via a physical bus providing voice and data communications over an Ethernet. Each subscriber is assigned a "home" voice mail unit. Incoming calls are notified to a control unit, along with information including the called number. The control unit uses this information to determine the home voice mail unit for the call, which is where the greeting for that subscriber is stored. The control unit then instructs a switching means to route the call through to the home unit. However, if the home unit is unavailable for some reason, for example it is already handling its maximum number of calls, then the control unit routes an incoming call to a different voice mail unit (a "remote" unit), along with an indication of which is the normal home unit for this subscriber. The remote unit can then try to retrieve the greeting for that subscriber from the home unit. After the remote unit completes the call, it can signal to the control unit that it has a message for that subscriber, which is not stored on the home unit for that subscriber. Somewhat similar systems are also disclosed in U.S. Pat. No. 5,301,226 and U.S. Pat. No. 5,394,460.
Another reason for linking voice mail systems together is when a firm for example has multiple locations, each with its own voice mail system. It then may be desired to allow subscribers at one location to send or forward voice mail messages from one location to another location. Two examples of this are U.S. Pat. No. 5,287,498 and U.S. Pat. No. 5,493,607, which provide a logical addressing scheme to be used with such multiple voice mail systems. Another example is WO 95/15046 which discusses the problem of how to provide a simple personalised greeting (in this case a subscriber speaking their own name), when a voice mail message is being sent to a remote voice mail system. One possibility mentioned is for each system to maintain a directory including information and a voice response for each user on each remote system in the network, but this is considered unattractive because of the storage and system administration requirements. The proposed solution is that when a message is sent to a subscriber on a remote voice mail system, this system returns the spoken name for that subscriber which is then stored locally, and so is available next time a message is to be sent to that caller. This is similar in concept to the familiar caching of data in a computer memory system, exploiting the observation that generally the subscribers most likely to be called in the future are those who have been called in the past. It should be noted that in U.S. Pat. No. 5,28,7498, U.S. Pat. No. 5,493,607 and WO 95/15046 it is the public telephone network which is primarily used for the transmission of voice messages between different voice mail systems.
EP-A-504880 describes a mail centre management system (eg for FAX or speech messages), having first and second mail devices connected by a network over which mail can be transferred between the devices.
Nevertheless, despite the above, there are still many situations in which the functionality of present day voice mail systems remains wanting. For example, to leave a voice mail message in a voice mailbox which is located on a voice mail system in a foreign country generally requires an international call. Some voice mail systems may allow international messaging between voice mail systems in different countries, but this is not available to callers who are not subscribers to that voice mail network. Moreover, many international corporations may have voice mail systems from different suppliers in different countries, and these are often incompatible with one another (eg they use different addressing schemes, or different voice compression formats), thereby preventing cross-border voice messaging.
Another difficulty is to provide 100% availability of voice mail systems to callers. The usual solution is to purchase a complex, expensive voice mail system with redundancy built in, but even these systems can be stretched if supplying the millions of voice mailboxes which may be required if the voice mail system is to be operated as a public voice mail facility by a telephone network company. Furthermore, such redundancy requirements may tie the operator to one vendor of voice mail equipment, and this may not always be desirable.
Another example of the limitations of present day systems is for example if a large multinational corporation wishes to provide a Freecall (800) number in multiple countries to allow employees and customers to leave voice messages for any corporation employees, no matter in which country the employees are located. However, if the corporation has different voice mail systems in different countries, and these are incompatible with one another, then the prior art provides no method for implementing such a service.
It is an object of the present invention to provide systems which address the limitations and disadvantages described above.